VDT stress mitigating device and method, VDT stress risk quantifying device and method, and recording medium

ABSTRACT

The aim of the present invention is to provide a VDT stress mitigating device and method capable of mitigating VDT stress caused by a regular spatial pattern and VDT stress caused by flicker generated by an interlaced format, a VDT stress risk quantifying device and method, and a recording medium. An A/D conversion section  10  imports interlaced format video signals P 1  from an external image signal output device and converts them in field units by A/D conversion into image data D 1 . A filter section  20 , while not distinguishing between the first field and the second field, and while maintaining the temporal order of these fields, performs a temporal filtering process on the image data of each field. A D/A conversion section  30  converts the image data D 2  that has undergone the temporal filtering process by the filter section  20  into image signals P 2  based on an interlaced format by D/A conversion. The image signals P 2  are then sequentially outputs according to the temporal order of the fields.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a VDT (video display terminal) stressmitigating device and method, a VDT stress risk quantifying device andmethod, and a recording medium for reducing VDT stress such as excessivestrain and fatigue caused by visual irritation.

The present application is based on an application for a patent in Japan(Japanese Patent Application Laid-Open (JP-A) No. 11-333429) and thecontents disclosed in the above Japanese patent application have beenincorporated as a portion of the present specification by reference.

2. Description of the Related Art

Conventionally, image display devices exist, as typified by televisionreceivers, for visually displaying information to people. Variousphysical symptoms caused by the use of these image display devices areknown as what is termed “VDT (video display terminal) stress disease”.Hitherto commonly known types of VDT stress include a reduction invisual ability and eyestrain due to long hours of continuously lookingat images displayed on an image display device. These types of stressare not connected to the content of the images themselves, but aremainly caused by the way in which the image display device is used.

In contrast, recent years have seen a diversification of graphicexpression that has accompanied technological advances in computergraphics and the like. The risk of content generated VDT stress that iscaused by the content of the graphics has been pointed out as a newmechanism of VDT stress. Graphic content that causes this type of VDTstress includes intraframe flicker, when a frame image in frequenciesbetween approximately 10 Hz to 30 Hz contained in the graphic contentflickers violently. There have been reports that, due to this type ofcontent generated VDT stress, excessive strain and fatigue is caused inthe cranial nervous system and the like, and that symptoms resemblingtravel sickness and, in some cases, even convulsions have been caused.

As a conventional technology for effectively preventing contentgenerated VDT stress, there are known a method and device forselectively attenuating temporal frequency components in theneighborhood of 10 Hz where content generated VDT stress most commonlyoccurs, such as is disclosed in Japanese Patent Application Laid-Open(JP-A) No. 07-101977 “VDT Stress Mitigating Method, Image FrequencyAttenuating Device, and VDT Adapter”.

However, in contrast to the aforementioned intraframe flicker in whichthe frame image flickers depending on the graphic content, even if thegraphic content does not involve a flicker phenomenon, as is the casewith a static image, then, as can be seen, for example, in the finelystriped pattern in the example shown in FIG. 14, the possibility hasbeen pointed out that content generated VDT stress may be caused inpeople who are predisposed to be hypersensitive to light even when thegraphic image is a regular spatial pattern in which the same shapes arearranged in a regular repetition within a space.

However, at present, there is no known technology for mitigating contentgenerated VDT stress caused by this type of regular spatial pattern orfor detecting the degree of risk of this type of VDT trouble.

Moreover, in the same way as with regular spatial patterns, even instatic images that do not contain any flicker phenomenon in the graphiccontent itself, when a stripe pattern in the direction of the scan line(horizontal stripes) is displayed at an interval equivalent to the scanline interval on an image display device having an interlaced format,such as NTSC, PAL, or the like, then flicker having a temporal frequencyof the frame frequency (30 Hz in NTSC, 25 Hz in PAL) is unexpectedlygenerated and, as a result, in some cases the same stress as contentgenerated VDT stress is generated.

Specifically, in an interlaced format, because the two fields that forma single frame are scanned at a frequency twice the frame frequency andthe two field images within the one frame are divided temporally anddisplayed in sequence, then, as is shown in FIG. 3 below, for example,when the graphic portions of the striped pattern (i.e. the blackportion) and the background portions belong to separate fields, thegraphic portions and the background portions are displayed alternately,and flicker having a temporal frequency of the frame frequency isgenerated.

According to the technology disclosed in the above JP-A 07-101977, it ispossible to suppress intraframe flicker. However, because thistechnology performs a temporal filtering process on each pixelindependently, it is not possible in principle to mitigate contentgenerated VDT stress caused by regular spatial patterns contained in thegraphics, or VDT stress caused by the aforementioned flicker generatedwhen field images are displayed alternately in an interlaced format.Moreover, nor is it possible to quantatively detect the risk of thistype of VDT stress.

SUMMARY OF THE INVENTION

The present invention was achieved in view of the above circumstances,and it is an objective thereof to provide a VDT (video display terminal)stress mitigating device and method capable of mitigating VDT stresscaused by a regular spatial pattern and VDT stress caused by flickergenerated by an interlaced format, a VDT stress risk quantifying deviceand method capable of quantatively ascertaining the risk of such VDTstresses, and a recording medium.

In order to achieve this objective, the present invention has thefollowing form.

That is, the first aspect of the present invention is a VDT stressmitigating device that is provided between an image signal output devicefor outputting image signals based on an interlaced format and an imagedisplay device for displaying an image based on the image signal, andperforms processing on the image signal in order to mitigate VDT stress,and comprises: filter means (for example, structural elementscorresponding to the A/D conversion section 10, the filter section 20,and the D/A conversion section 30, each of which is described below) forperforming a temporal filtering process on the image signals of each ofa first and second field without any distinction being made between thefirst and second fields and while the temporal order of these fields ismaintained.

The second aspect of the present invention is the VDT stress mitigatingdevice according to the first aspect of the present invention, whereinthe filter means comprises: a signal importing section (for example, astructural element corresponding to the A/D conversion section 10described below) for sequentially importing the image signals in unitsof fields; a low pass filter section (for example, a structural elementcorresponding to the filter section 20 described below) for attenuatingpredetermined frequency components contained in the image signals; and asignal output section (for example, a structural element correspondingto the D/A conversion section 30 described below) for sequentiallyoutputting in accordance with the temporal order the image signals thathave undergone the predetermined frequency component attenuation.

The third aspect of the present invention is the VDT stress mitigatingdevice according to the first aspect of the present invention, whereinthe filter section comprises: a signal importing section (for example, astructural element corresponding to the A/D conversion section 10described below) for sequentially importing the image signals in unitsof fields; a risk quantifying section (for example, a structural elementcorresponding to the risk quantifying section 100 described below) forquantifying a risk by calculating an index value representing a risk ofVDT stress due to the image signals; a low pass filter section (forexample, a structural element corresponding to the filter section 200described below) for attenuating predetermined frequency componentscontained in the image signals and reflecting the index value such thatthe risk is suppressed; and a signal output section (for example, astructural element corresponding to the D/A conversion section 30described below) for sequentially outputting in accordance with thetemporal order the image signals that have undergone the predeterminedfrequency component attenuation.

The fourth aspect of the present invention is the VDT stress mitigatingdevice according to the first aspect of the present invention, whereinthe filter means comprises: a signal importing section (for example, astructural element corresponding to the A/D conversion section 10described below) for sequentially importing the image signals in unitsof fields; a field dividing section (for example, a structural elementcorresponding to the field dividing section 15 described below) fordividing each field of the image signals into a plurality of sub-fields;a low pass filter section (for example, a structural elementcorresponding to the filter section 20 described below) for performing atemporal filtering process on image signals of each sub-field withoutdistinguishing between the plurality of sub-fields and while maintainingthe temporal order of the sub-fields, and for attenuating predeterminedfrequency components contained in an image formed by the image signals;a field synthesizing section (for example, a structural elementcorresponding to the field synthesizing section 25 described below) forsynthesizing image signals of each field from image signals of eachsub-field in which the predetermined frequency components have beenattenuated; and a signal output section (for example, a structuralelement corresponding to the D/A conversion section 30 described below)for sequentially outputting in accordance with the temporal order theimage signals of each field that have been synthesized by the fieldsynthesizing section.

The fifth aspect of the present invention is a VDT stress riskquantifying device for quantifying a risk of VDT stress due to imagesignals based on an interlaced format, comprising: a signal holdingsection (for example, a structural element corresponding to the fieldmemory 101 described below) for importing and temporarily holding theimage signals; a low pass filter section (for example, a structuralelement corresponding to the low pass filter 102 described below) forperforming a temporal filtering process on image signals of a firstfield and a second field without distinguishing between each field andwhile maintaining the temporal order of the fields, and for attenuatingpredetermined frequency components contained in an image formed by theimage signals; and a calculating section (for example, a structuralelement corresponding to the risk index value calculator 103 describedbelow) or calculating index values representing the risk based on adifference between image signals that have undergone a temporalfiltering process by the low pass filter section and image signals heldin the signal holding section.

The sixth aspect of the present invention is the VDT stress mitigatingdevice according to any of the second through fourth aspects of thepresent invention, wherein the low pass filter section attenuatestemporal frequency components that are contained in an image formed bythe image signals and that are equivalent to a frame scan frequency.

The seventh aspect of the present invention is the VDT stress mitigatingdevice according to the second aspect of the present invention, whereinthe low pass filter section attenuates spatial frequency components thatare contained in an image formed by the image signals and that are thehighest spatial frequency components in a direction orthogonal to a scanline direction on a device on which the image is displayed.

The eighth aspect of the present invention is the VDT stress mitigatingdevice according to the second aspect of the present invention, whereinthe signal importing section is provided with an A/D conversion functionfor receiving analog quantity image signals input from the image signaloutput device, converting the analog quantity image signals into digitalquantity image data, and outputting this to the low pass filter, andwherein the signal output section is provided with a D/A conversionfunction for converting digital quantity image data output from the lowpass filter section into analog quantity image signals based on aninterlaced format.

The ninth aspect of the present invention is the VDT risk stressquantifying device according to the fifth aspect of the presentinvention, wherein the low pass filter section attenuates temporalfrequency components that are contained in an image formed by the imagesignals and that are equivalent to a frame scan frequency.

The tenth aspect of the present invention is the VDT risk stressquantifying device according to the fifth aspect of the presentinvention, wherein the low pass filter section attenuates spatialfrequency components that are contained in an image formed by the imagesignals and that are the highest spatial frequency components in adirection orthogonal to a scan line direction on a device on which theimage is displayed.

The eleventh aspect of the present invention is a VDT stress mitigationmethod for mitigating VDT stress by attenuating predetermined frequencycomponents of image signals based on an interlaced format, comprisingthe following steps: (a) a signal importing step (for example, anelement corresponding to step S1 described below) in which the imagesignals are sequentially imported in units of fields; (b) a filteringstep (for example, an element corresponding to step S2 described below)in which a temporal filtering process is performed on image signals of afirst field and a second field without distinguishing between each fieldand while maintaining the temporal order of the fields, and forattenuating predetermined frequency components contained in an imageformed by the image signals; and (c) a signal output step (for example,an element corresponding to step S3 described below) in which imagesignals that have undergone the temporal filtering process aresequentially output in accordance with the temporal order.

The twelfth aspect of the present invention is a VDT stress mitigationmethod for mitigating VDT stress by attenuating predetermined frequencycomponents of image signals based on an interlaced format, comprisingthe following steps: (a) a signal importing step (for example, anelement corresponding to step S21 described below) in which the imagesignals are sequentially imported in units of fields; (b) a quantifyingstep (for example, an element corresponding to step S22 described below)in which a risk is quantified by calculating an index value representingthe risk of VDT stress due to the image signals; (c) a filtering step(for example, elements corresponding to steps S23 and S24 describedbelow) in which the index value is reflected and a temporal filteringprocess is performed on image signals of a first field and a secondfield without distinguishing between each field and while maintainingthe temporal order of the fields such that the risk is suppressed, andpredetermined frequency components contained in an image formed by theimage signals are attenuated; and (d) a signal output step (for example,an element corresponding to step S25 described below) in which imagesignals that have undergone the temporal filtering process aresequentially output in accordance with the temporal order.

The thirteenth aspect of the present invention is a VDT stressmitigation method for mitigating VDT stress by attenuating predeterminedfrequency components of image signals based on an interlaced format,comprising the following steps: (a) a signal importing step (forexample, an element corresponding to step S31 described below) in whichthe image signals are sequentially imported in units of fields; (b) afield dividing step (for example, an element corresponding to step S32described below) in which each field of the image signals is dividedinto a plurality of sub-fields; (c) a filtering step (for example, anelement corresponding to step S33 described below) in which a temporalfiltering process is performed on image signals of each sub-fieldwithout distinguishing between the plurality of sub-fields and whilemaintaining the temporal order of the sub-fields, and for attenuatingpredetermined frequency components contained in an image formed by theimage signals; (d) a field synthesizing step (for example, an elementcorresponding to step S34 described below) for synthesizing imagesignals of each field from image signals of each sub-field in which thepredetermined frequency components have been attenuated; and (e) asignal output step (for example, an element corresponding to step S35described below) in which synthesized image signals of each field aresequentially output in accordance with the temporal order.

The fourteenth aspect of the present invention is a VDT stress riskquantifying method for quantifying a risk of VDT stress due to imagesignals based on an interlaced format, comprising the following steps:(a) a signal importing step (for example, an element corresponding tostep S10 described below) in which the image signals are sequentiallyimported in units of fields; (b) a signal holding step (for example, anelement corresponding to step S11 described below) for holding the imagesignals; (c) a filtering step (for example, an element corresponding tostep S12 described below) in which a temporal filtering process isperformed on image signals of a first field and a second field withoutdistinguishing between each field and while maintaining the temporalorder of the fields, and for attenuating predetermined frequencycomponents contained in an image formed by the image signals; and (d) acalculating step (for example, an element corresponding to step S13described below) in which index values representing the risk arecalculated based on a difference between image signals that haveundergone the temporal filtering process and the held image signals.

The fifteenth aspect of the present invention is the VDT stressmitigation method according to the eleventh through thirteenth aspectsof the present invention, wherein, in the filtering step, temporalfrequency components that are contained in an image formed by the imagesignals and that are equivalent to a frame scan frequency areattenuated.

The sixteenth aspect of the present invention is the VDT stressmitigation method according to the eleventh through thirteenth aspectsof the present invention, wherein, in the filtering step, spatialfrequency components that are contained in an image formed by the imagesignals and that are the highest spatial frequency components in adirection orthogonal to a scan line direction on a device on which theimage is displayed are attenuated.

The seventeenth aspect of the present invention is the VDT stress riskquantifying method according to the fourteenth aspect of the presentinvention, wherein, in the filtering step, temporal frequency componentsthat are contained in an image formed by the image signals and that areequivalent to a frame scan frequency are attenuated.

The eighteenth aspect of the present invention is the VDT stress riskquantifying method according to the fourteenth aspect of the presentinvention, wherein, in the filtering step, spatial frequency componentsthat are contained in an image formed by the image signals and that arethe highest spatial frequency components in a direction orthogonal to ascan line direction on a device on which the image is displayed areattenuated.

The nineteenth aspect of the present invention is a computer readablerecording medium on which a program for mitigating VDT stress byattenuating predetermined frequency components of image signals based onan interlaced format is recorded, the program comprising the followingsteps: (a) a signal importing step in which the image signals aresequentially imported in units of fields; (b) a filtering step in whicha temporal filtering process is performed on image signals of a firstfield and a second field without distinguishing between each field andwhile maintaining the temporal order of the fields, and for attenuatingpredetermined frequency components contained in an image formed by theimage signals; and (c) a signal output step in which image signals thathave undergone the temporal filtering process are sequentially output inaccordance with the temporal order.

The main operation of the present invention will now be described.

According to the present invention, image signals based on an interlacedformat undergo temporal a filtering process in a first and second field,with the temporal order of the fields being maintained, and with nodistinction made between the first and second field and each field beingtreated as equal to the other. Specifically, the line positions of afirst field and second field forming one frame are different to eachother. However, in the temporal filtering process, this difference inthe line positions is ignored. As a result, the first field and secondfield are treated as forming temporally continuous images in the samespace, and the image signals of each field are made the subjects of thetemporal filtering process equally to each other.

At this time, as a result of the temporal filtering process beingperformed with no distinction being made between the first and secondfields, the images interfere with each other between the first andsecond field so that, in addition to the temporal filtering process, aspatial filtering process is also performed, allowing both temporal andspatial filtering processes to be performed. Consequently, predeterminedfrequency components contained in an image are attenuated temporally orspatially. After the temporal filtering process has been performed, theimage signals are output according to the temporal order of the fields.As a result of the above, image signals, in which those predeterminedfrequency components that cause VDT stress have been attenuated, areobtained, and VDT stress is mitigated.

The above invention can also be described as follows.

Specifically, the present invention is a VDT stress mitigation methodfor mitigating VDT stress caused by flicker equal to the frame scanfrequency generated by the display of images having a pattern of equallypitched stripes parallel to the scan line direction in a display devicefor interlaced scan format video signals. This VDT stress mitigationmethod is characterized in that, by sending the two fields forming eachframe of the interlaced image signals to the same field memory andperforming a temporal frequency low pass filtering process in a temporalfrequency twice that of the frame frequency, an interlaced format videosignal image is converted into an image in which the high temporalfrequency power components and the high spatial frequency powercomponents have been attenuated simultaneously.

Moreover, the present invention is a VDT stress mitigating device thatis provided between an image signal output device for outputtinginterlaced scan format video signals and the image display devicethereof, for mitigating VDT stress caused by flicker equal to the framescan frequency generated by the display of images having a pattern ofequally pitched stripes parallel to the scan line direction. This VDTstress mitigating device is characterized in that, by sending the twofields forming each frame of the interlaced image signals to the samefield memory and performing a temporal frequency low pass filteringprocess in a temporal frequency twice that of the frame frequency, aninterlaced format video signal image is converted into an image in whichthe high temporal frequency power components and the high spatialfrequency power components have been attenuated simultaneously.

Further, the present invention is a VDT stress mitigation for mitigatingVDT stress caused by the display of images having a regular spatialpattern, and is characterized in that, by performing a load addition forpixels adjacent to each pixel in the image, the image is converted intoan image in which the highest spatial frequency components that can bedisplayed on the display device are attenuated.

Furthermore, the present invention is a VDT stress mitigating devicethat is provided between an image signal output device and an imagedisplay device for mitigating VDT stress caused by the display of imageshaving a regular spatial pattern, and is characterized in that, byperforming a load addition for pixels adjacent to each pixel in theimage, the image is converted into an image in which the highest spatialfrequency components that can be displayed on the display device areattenuated.

According to the present invention, the power of spatial frequencycomponents that are contained in moving images or static images on adisplay device and are the highest spatial frequency components in adirection orthogonal to the scan line direction capable of beingdisplayed on that display device is detected. In addition, the power oftemporal frequency components equivalent to the frame scan frequency ofinterlaced scan format video signals displayed on the display device isdetected. Then on the basis of this, the power of the highest spatialfrequency components in a direction orthogonal to the scan linedirection capable of being displayed on the display device and that arecontained in the displayed images, and the power of temporal frequencycomponents equivalent to the frame scan frequency of interlaced scanformat video signals displayed on the display device are attenuated. Asa result, content generated VDT stress caused by flicker generated byfine striped patterns in a direction orthogonal to the scan linedirection and fine striped patterns, having an equal pitch and parallelto the scan line, are mitigated. In addition, the risk of VDT stresscaused by the power of the highest spatial frequency components in adirection orthogonal to the scan line direction capable of beingdisplayed on the display device, and the power of temporal frequencycomponents equivalent to the frame scan frequency is quantified.

In this way, according to the present invention, the size of the powerof flicker components of a temporal frequency equivalent to the framescan frequency generated by images having a pattern of equally pitchedstripes parallel to a horizontal scan line of a display device fordisplaying interlaced format graphic signals is detected. By thenappropriately attenuating the power of these components according to theabove size, excessive stress on a person viewing the video displaydevice is reduced, and it is possible to prevent any harmful healtheffects arising therefrom.

Note that this outline of the present invention does not list allnecessary features and, consequently, sub-combinations of the featureslisted here are also considered as belonging to the scope of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of the VDT stressmitigating device according to the first embodiment of the presentinvention.

FIG. 2 is a flow chart showing the flow of operation of the VDT stressmitigating device according to the first embodiment of the presentinvention.

FIG. 3 is an explanatory view for describing the operation of the filterportion (the contents when the field is not distinguished) according tothe first embodiment of the present invention.

FIG. 4 is an explanatory view for describing the operation of the filterportion (the contents when the temporal sequence is maintained)according to the first embodiment of the present invention.

FIG. 5 is a characteristic view for describing the characteristics ofthe filter portion according to the first embodiment of the presentinvention.

FIG. 6 is a block diagram showing the structure of the VDT stress riskquantifying device according to the second embodiment of the presentinvention.

FIG. 7 is a flow chart showing the flow of operation of the VDT stressrisk quantifying device according to the first embodiment of the presentinvention.

FIG. 8 is a block diagram showing the structure of the VDT stressmitigating device according to the third embodiment of the presentinvention.

FIG. 9 is a flow chart showing the flow of operation of the VDT stressmitigating device according to the third embodiment of the presentinvention.

FIG. 10 is a diagram showing the blurring constant calculated by theblurring constant calculator according to the third embodiment of thepresent invention.

FIG. 11 is a block diagram showing the structure of the VDT stressmitigating device according to the fourth embodiment of the presentinvention.

FIG. 12 is a flow chart showing the flow of operation of the VDT stressmitigating device according to the fourth embodiment of the presentinvention.

FIG. 13 is an explanatory view for describing the operating principle ofthe VDT stress mitigating device according to the fourth embodiment ofthe present invention.

FIG. 14 is a diagram showing an example of a regular spatial pattern (astriped pattern) that causes VDT stress.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the embodiments of the present invention will be described withreference made to the drawings.

The embodiments described below in no way limit the invention accordingto the claims.

Moreover, it is not absolutely necessary for all the features describedin the embodiments to be combined together in order to achieve theobjectives.

§ 1. First Embodiment

First, the first embodiment of the present invention will be described.

The VDT stress mitigating device according to the first embodiment isinstalled between an image signal output device such as a video tunerand an image display device such as a video monitor, and, withoutdistinguishing between the first field and second field, performs atemporal filtering process for each field on a video signal (imagesignal) based on an interlaced format such as NTSC or PAL.

FIG. 1 shows the structure of the VDT stress mitigating device accordingto the first embodiment. In FIG. 1, the symbol 10 denotes an A/Dconversion section. The A/D conversion section 10 sequentially importsanalog quantity video signals P1 based on an interlaced format from anunillustrated external image signal output device in field units, andconverts these to digital quantity image data (numerical data) D1 by A/Dconversion. The symbol 20 denotes a filter section comprising low passfilters 21 to 24 connected in multistage. The filter section 20attenuates predetermined frequency components (those frequencycomponents that contribute to VDT stress) by implementing a temporalfiltering process on the image data D1 while maintaining the temporalsequence of each field without distinguishing between the first fieldand the second field. The symbol 30 denotes a D/A conversion section.The D/A conversion section 30 performs D/A conversion on digitalquantity image data (numerical data) D2 on which a temporal filteringprocess has been performed by the filter section 20 thus converting itto an analog quantity video signal P2 based on an interlaced format.

Next, the operation of the VDT stress mitigating device according to thefirst embodiment will be described according to the routine flow shownin FIG. 2. Note that, in the description below, the term “image signal”refers to a concept that encompasses both analog quantity “videosignals” and digital quantity “image data”.

First, in step S1, the A/D conversion section 10 sequentially importsanalog quantity video signals P1 in an interlaced format from anunillustrated external image signal output device, quantizes these withfields as units, and performs A/D conversion so that the video signalsP1 of each field are converted into digital quantity image data D1. Whenthe video signals are in NTSC format, the temporal frequency in frameunits is 30 frames per second. Because one frame is formed from both afirst field and a second field, the temporal frequency of the videosignals in field units becomes 60 fields per second (i.e. twice 30).Accordingly, in this case, in one second, video signals P1 for 60 fieldsare imported and converted to image data D1. The image data D1 for eachfield is transferred in sequence to the filter section 30.

In step S2 the filter section 20 performs a temporal filtering processon the image data D1 of each field transferred from the A/D conversionsection 10. At this time, the filter section 20 performs the temporalfiltering process on the image data of each field while maintaining thetemporal sequence of each field without distinguishing between the firstfield and the second field forming each frame. That is, the images ofeach field are treated as field images undistinguished from each other,and the filtering process is performed in accordance with the temporalsequence.

At this point, a supplementary explanation will be given on what ismeant by the filter section 20 not distinguishing between the firstfield and the second field with reference made to FIG. 3.

As is shown in the example in FIG. 3, one frame comprises a first fieldthat contains the odd numbered lines L11 to L14 and a second field thatcontains the even numbered lines L21 to L24, and the line position isdifferent for each field within a frame. Thus the first field and thesecond field can be distinguished by the fact that their line positionsare different. However, in the temporal filtering process, the filterportion 20 ignores this difference in the line positions and regards theodd numbered lines L11 to L14 in the same way as the even numbered linesL21 to L24. As a result, it makes no distinction between the first fieldand the second field and treats the images of each field as field imagesthat are undistinguished from each other.

This is to say that the fact that no distinction is made between thefirst field and second field means that the first field and second fieldare treated as both showing an image on the same hypothetical line. Forexample, the odd numbered line L11 and the even numbered line L21 inFIG. 13 are treated as the same line, and equivalent lines in thecorresponding sequence in each field are regarded in the same way. Bynot distinguishing between fields in this way, it becomes possible toperform a common temporal filtering process for each of the fieldsforming one frame.

Next, a supplementary explanation of what is meant by the filter section20 maintaining the temporal order of each field will be given withreference made to FIG. 4.

In FIG. 4, the symbols F1 to Fn (where n=a natural number) representframes, the symbols f11, f12, ˜, fn1, and fn2 represent the fieldbelonging to each frame. Therefore, in an interlaced format, the framesF1 to Fn are scanned according to the temporal order and after the firstfield has been scanned, the second field is scanned for each frame.

As is shown in the example in FIG. 4, the temporal order of each fieldis as follows. Specifically, the first field f11 belonging to theleading frame F1, the second field f12 belonging to the same frame F1,the first field f21 belonging to the next frame F2, the second field f22belonging to the same frame F2, the first field f31 belonging to thenext frame F3, the second field f32 belonging to the same frame F3, andso on down to the first field fn1 belonging to the last frame Fn, andthe second field fn2 belonging to the same frame Fn2.

In this way, the filter portion 20 does not distinguish between thefirst field and second field and performs a temporal filtering processon each field in accordance with the above temporal of each field (whilemaintaining the field temporal order), as is described below.

The temporal filtering process of the filter section 20 will now bedescribed.

The low pass filter 21 provided in the first stage of the filter section20 calculates by sum of product calculation the field image data1I_(i)(t) after the temporal filtering process from the image dataI_(i)(t) output from the A/D conversion section 10, using the functionF_(δ)shown in Formula (1) below.¹ I _(i)(t)=¹ F _(δ)(I _(i)(t))=(1−δ)×I _(i)(t)+δ×I _(i)(t−Δt)   (1)

In Formula (1), i represents the coordinates of pixels within each fieldimage data; Δt represents the temporal interval between the twosuccessively input fields and is one 60th of a second when the videosignal is in the NTSC format. δ is a constant that determines thecharacteristics of the low pass filters and is a constant greater than 0and less than 1, for example, it may be set as 0.7. As is describedbelow, because of visual blurring that occurs in an image in accordancewith this constant δ, δ is referred to in the description below as theblurring constant.

The image data ¹I_(i)(t) obtained by the low pass filter 21 istransferred as in a sequential pipeline to the second stage andfollowing low pass filters 22, 23, and 24. In the low pass filters ofeach of these stages, the temporal filtering process using theequivalent function 1F_(δ) as for the low pass filter 21 is performed.

When the low pass filter performing the temporal filtering process usingthe function ¹F_(δ) connects to the nth stage, the image data^(n)I_(i)(t) obtained from the final low pass filter is obtained usingthe following Formula (2).^(n) I _(i)(t)=^(n) F _(δ)(I _(i)(t))=(1−δ)×^(n-1) F _(δ)(^(i-1) I_(i)(t))+δ×^(n-1) F _(δ)(^(i-1) I _(i)(t))   (1)

At this point, the relationship between the above temporal filteringprocess and VDT stress will be described.

According to Formula (1), the image data I_(i)(t) from the current fieldand the image data I_(i)(t−Δt) from the previous field are added after aweighting in accordance with the blurring constant δ has been applied (aconvolution calculation), so that earlier image data is reflectedaccumulatively relative to the current image data. As a result, thehigher frequencies that contain the frequencies of the flicker generatedin the interlaced format (i.e. the frame scan frequencies) areattenuated from out of the temporal frequency components of each fieldimage, and flicker in these frequencies is thus suppressed. At thistime, visually, blurring is generated in the image between the firstfield and second field, and the degree of the change in the imagebetween fields is suppressed. Consequently, VDT stress caused by thisflicker is mitigated.

Moreover, as described above, in the present embodiment, because acommon temporal filtering process is performed on each field without anydistinction being made the first field and second field whose linepositions are different to each other, as a result of the image data ofboth the first field and second field being accumulatively reflectedtogether between the fields, a spatial filtering process is alsoimplemented. Therefore, the highest spatial frequency components in adirection orthogonal to the direction of the scan line are attenuatedand the degree of spatial changes is suppressed visually. Accordingly,VDT stress caused by regular spatial patterns such as a striped patternis mitigated.

Note that the highest spatial frequency components in a directionorthogonal to the direction of the scan line correspond, for example, tothe pitch of the scan line.

The relationship between the blurring constant δ and the filterattenuation characteristics when the low pass filter is connected forone stage and when the low pass filter is connect for several stages isshown in FIG. 5. As is shown in FIG. 5, if the blurring constant δ isincreased, the characteristics move towards the lower frequencies. Inorder to mitigate VDT stress, it is possible to attenuate the higherfrequencies. However, if the higher frequencies are attenuated byincreasing the blurring constant δ, then a portion of the useful lowerfrequencies are sacrificed. In contrast, as is the case with the filtersection 20 according to the first embodiment, if the low pass filter isformed in several stages, then as is shown by the broken line in FIG. 5,the selectivity of the filter is improved. As a result, the sacrifice ofthe lower frequency regions can be kept to a minimum and the higherfrequency regions attenuated effectively. This allows the effectimparted to the image quality to be suppressed.

In the manner described above, the filter section 20 performs a temporalfiltering process on the image data D1 output from the A/D conversionsection 10 and outputs image data D2 in which predetermined frequencycomponents that contribute to VDT stress (such as frame scan frequencycomponents and the highest spatial frequency components in a directionorthogonal to the direction of the scan line) have been attenuated.

Next, the D/A conversion section 30 performs a D/A conversion on theimage data D2 obtained from the filter section 20 so that this isconverted into interlaced format video signals P2 that are then output.At this time, the D/A conversion section 30 successively converts theimage data of each field successively output from the filter section 20into field analog signals. These are then reconstructed as video signalsbased on an interlaced format in accordance with the temporal order ofeach field and are successively output. At this time, for example, videosignals of the first field that have been processed ahead of the videosignals of the second field by the A/D converter 10 are output ahead ofthe video signals of the second field in the D/A converter 30, therebymaintaining the temporal order.

As a result of the above, a series of processes are performed oninterlaced format video signals output from an external image signaloutput device in order to mitigate VDT stress. These video signals arethen output to an unillustrated image display device.

The effects of the first embodiment are summarized below.

(1) According to the first embodiment, it is possible to attenuate thehighest spatial frequency components (for example, the spatial frequencycomponents of regular spatial patterns such as finely striped patterns)in a direction orthogonal to the scan line direction capable of beingdisplayed on an image display device, and it is possible to mitigatecontent generated VDT stress caused by this type of regular spatialpattern.

(2) Further, it is possible to mitigate content generated VDT stresscaused by images having a pattern of equally pitched stripes parallel toa horizontal scan line, that is, by flicker generated in a temporalfrequency half the frame frequency when a striped pattern is displayed.

(3) Further, it is possible to also attenuate temporal frequencycomponents of approximately 10 Hz contained in the graphic content, andto also mitigate VDT stress caused by images flickering in a frequencyof approximately 10 Hz.

(4) Further, it is possible to suppress the amount of memory required tostore the image data in each low pass filter to half that when theprocessing is performed in frame units by performing the temporalfiltering process in field units.

Note that, in the first embodiment, the blurring constant δ was set incommon for the low pass filters 21, 22, 23, and 24 forming the filtersection 20. However, it is also possible to employ a different blurringconstant for each low pass filter.

Moreover, in the first embodiment, the number of low pass filter stagesin the filter section 20 was set at four. However, the number of stagesmay be reduced to three or less, or may be increased to five or more. Inaddition, the number of low pass filter stages and the blurring constantδ may be set appropriately, in accordance with the necessary filtercharacteristics.

Furthermore, in the first embodiment, the VDT stress mitigating devicewas installed between an image signal output device such as a videotuner or the like and an image display device such as a video monitor orthe like. However, the present invention is not limited to this, and theimage signal output device and image display device may be integrated asa single device. Moreover, the image signal output device is not limitedto a video tuner and any device that outputs an interlaced scan formatanalog video signal in NTSC, PAL, or the like, for example, a video tapeplayback device, a laser disk playback device, or a TV game device maybe used. In addition, any device may be used as the image display deviceprovided that it receives interlaced scan format analog video signals asinput signals.

Furthermore, in the first embodiment, analog quantity video signals P1are converted into digital quantity image data D1 by the A/D converter10, and digital quantity image data D2 is converted into analog quantityvideo signals P2 by the D/A converter 30. However, if a device forinputting and outputting digital image signals is connected, the A/Dconversion function of the A/D conversion section 10 and the D/Aconversion function of the D/A conversion section 30 are not needed, anda structure may be formed in which image data from the first field andthe second field is input in time series order and a filtering processis performed in the same way by the common filter section 20.

Furthermore, in the first embodiment, the field image data ¹I_(i)(t) wascalculated after the temporal filtering process from the image dataI_(i)(t) of the current field and the image data I_(i)(t−Δt) from theprevious field by each low pass filter forming the filter section 20.However, the present invention is not limited to this. This means thatit is also possible to perform the temporal filtering process whileconsidering the image data from the field prior to that. In this case,by selecting the weighting coefficient for the image data belonging toeach field, it becomes possible to finely control the filtercharacteristics and to set even more appropriate filter characteristics.

§ 2. Second Embodiment

The second embodiment of the present invention will be described next.

The second embodiment deals with a VDT stress risk quantifying devicefor quantifying and detecting the risk of VDT stress caused by imagesbased on an interlaced format such as NTSC or PAL.

FIG. 6 shows the structure of the VDT stress risk quantifying deviceaccording to the second embodiment. In FIG. 6, the symbol 10 refers toan A/D conversion section. The A/D conversion section 10 sequentiallyimports from the outside in field units analog quantity video signals P1based on an interlaced format and converts these into image data D1 byA/D conversion.

The symbol 100 refers to a risk quantifying section forming the featureportion of the VDT stress risk quantifying device according to thesecond embodiment. The risk quantifying section 100 comprises: fieldmemory 101 for importing the image data D1 of a single field andtemporarily holding it; a low pass filter 102 for performing a temporalfiltering process on the image data D1; and a risk index calculator 103for calculating a risk index value e(t) using both sets of image datafrom before and after the temporal filtering process.

Next, the operation of the VDT stress risk quantifying device accordingto the second embodiment will be described according to the flow of theroutine shown in FIG. 7.

First, in step S10, the A/D conversion section 10 sequentially importsanalog quantity video signals P1 in an interlaced format from anunillustrated external image signal output device, quantizes these withfields as units, and performs A/D conversion so that the video signalsof each field are converted into digital quantity image data D1. Theimage data D1 is then transferred to the risk quantifying section 100.

Next, in step S11, the field memory 101 sequentially imports the imagedata D1 of one field that has been converted by the A/D conversionsection 10 and temporarily holds it. The contents of the field memory101 are sequentially updated to the image data of the new field importedfrom the A/D conversion section 10.

Next, in step S12, in the risk quantifying section 100 to which theimage data D1 has been transferred, the low pass filter 102 of the riskquantifying section 100 performs a temporal filtering process on theimage data D1. At this time, the low pass filter 102 functions in thesame way as, for example, the low pass filter 21 according to the firstembodiment. That is, the low pass filter 102 performs a temporalfiltering process while maintaining the temporal order of each fieldwithout distinguishing between the first field and second field formingone frame. As a result, predetermined frequencies contained in the imageformed by the image data D1 are attenuated.

Next, in step 13, the risk index calculator 103 receives the image datafrom the low pass filter 102 after the image data has undergone thetemporal filtering process, and also reads from the field memory 101 theimage data that corresponds to this image data before the temporalfiltering process. The risk index value e(t) is calculated using Formula(3) below, based on the difference between the image data before thetemporal filtering process and the image data after the temporalfiltering process.

[number 1]

In this case, w_(c) represents the loads w_(R), w_(G), and w_(B) foreach of the color components R (red), G (green), and B (blue), and isset as, for example, w_(R)=w_(G)=w_(B)=1.0. Imax is the maximum value ofthe image data in each pixel of the field, and, for example, is set as255 when the data of each pixel is expressed in 8 bit. N represents thetotal number of the image data of a single field (i.e. the total numberof pixels in a single field), and when a single frame comprises 640×480pixels, for example, the total number N of the image data of a singlefield is set as 153600 (=640×240). m is an index for expressing thenon-linearity of the human sensitivity to the risk of VDT stress, andany one of, for example, 1, 2, or 3 may be set as the index m.

In Formula (3), by setting the load in accordance with each of the colorcomponents R, G, and B, the risk is quantified in accordance with thedifference in color in the image. Generally, red is most likely to causeVDT stress. Therefore, the loads w_(R), w_(G), and w_(B) are setappropriately such that, compared with the other colors, red is sizablyreflected in the risk index value e(t). Moreover, by normalizing usingthe total number N of the image data, the effect on the risk index valuee(t) of any differences in the size and the like of the screens of thedisplay devices is eliminated, and it is possible to determine the riskof VDT stress in an image on any screen based on the same standard.

Note that, in Formula 3, time is required in the calculation because ofthe floating point arithmetic calculation for the termΣw_(C)|I_(i)(t)−1I_(i)(t)|^(m). Therefore, values that can be set forthis term are calculated in advance and set in table form. When the riskindex e (t) is calculated, if it is possible to acquire values for thisterm by referring to this table, then the time needed for thecalculation of the risk index value e(t) can be effectively shortened.

As described above, the risk index calculator 103 determines thedifference before and after the temporal filtering process by setting aload in accordance with R, G, and B for all of the pixels on a screenusing the above formula (3). The risk index e(t) is then calculated bynormalizing this difference using the total number N of image data of asingle field, the maximum value I_(max) of the image data, and the loadw_(c).

Note that, in the second embodiment, the field memory 101 imports theimage data D1 from the A/D conversion section 10, and sequentiallyoutputs it together with the risk index value e(t) to the outside asimage data D10. As a result, as in the third embodiment described below,it is possible to reflect the risk index value e(t) and provide thenecessary information to the device that performs the temporal filteringprocess in the image signal.

The effects of the second embodiment are summarized below.

(1) According to the second embodiment, it is possible to quantify anddetect the risk of content generated VDT stress caused by regularspatial patterns having the highest spatial frequency components (forexample, the spatial frequency components of regular spatial patternssuch as finely striped patterns) in a direction orthogonal to the scanline direction capable of being displayed on an image display device.

(2) Further, it is possible to quantify and detect the risk of contentgenerated VDT stress caused by images having a pattern of equallypitched stripes parallel to a horizontal scan line, that is, by flickergenerated in a temporal frequency half the frame frequency when astriped pattern is displayed.

(3) Further, it is possible to also attenuate temporal frequencycomponents of approximately 10 Hz contained in the graphic content, andto also quantify and detect the risk of VDT stress caused by imagesflickering in a frequency of approximately 10 Hz.

(4) Further, it is possible to suppress the amount of memory required tostore the image data in the low pass filter 102 to half that when theprocessing is performed in frame units by performing the temporalfiltering process in field units.

Note that, in the second embodiment, the one stage low pass filter 102was employed. However, it is also possible to increase the number ofstages to two or more, and it is also possible to appropriately set thenumber of low pass filter stages in accordance with the necessary filtercharacteristics. In this case, either a common blurring constant δ maybe employed for each low pass filter, or a different blurring constantmay be employed for each filter. It is also possible to select eachblurring constant δ in accordance with the necessary filtercharacteristics.

Moreover, in the second embodiment, analog quantity video signals P1 areconverted into digital quantity image data D1 by the AID converter 10.However, if a device for outputting digital image signals is connected,the A/D conversion function of the A/D conversion section 10 is notneeded, and a structure may be formed in which image data from the firstfield and the second field is input in time series order and a filteringprocess is performed in the same way by the common filter section 20.

Furthermore, in the second embodiment, the field image data ¹I_(i)(t)was calculated after the temporal filtering process from the image dataI_(i)(t) of the current field and the image data I_(i) (t−Δt) from theprevious field by the low pass filter 102. However, the presentinvention is not limited to this. That is, it is also possible toperform the temporal filtering process while considering the image datafrom the field prior to that. In this case, by selecting the weightingcoefficient for the image data belonging to each field, it becomespossible to finely control the filter characteristics and to calculatethe risk index value e(t) even more appropriately.

§ 3. Third Embodiment

The third embodiment of the present invention will be described next.

In the third embodiment of the present invention, the functions of therisk quantifying device of the second embodiment are given to the VDTstress mitigating device according to the first embodiment, therebyallowing the risk index value e(t) to be reflected in the blurringconstant δ, and enabling the filter characteristics to be appropriatelycontrolled in accordance with the degree of risk of VDT stress.

The structure of the VDT stress mitigating device according to the thirdembodiment is shown in FIG. 8. In FIG. 8, the symbol 10 denotes an A/Dconversion section the same as that described in the first embodiment.The A/D conversion section 10 converts interlaced format image signalsP1 into image data D1 by A/D conversion and then outputs the image dataD1. The symbol 100 denotes a risk quantifying section having the samestructure as that described in the second embodiment (see FIG. 6). Therisk quantifying section 100 quantifies the risk of VDT stress as a riskindex value e(t). The symbol 150 denotes a blurring constant calculatorfor calculating a blurring constant δ used in the temporal filteringprocess. The blurring constant calculator 150 reflects the risk indexvalue e(t) as it calculates the blurring constant δ.

The symbol 200 denotes a filter section comprising low pass filters 201to 204 connected in multistage. The filter section 200 performs atemporal filtering process on the image data D1 using a blurringconstant obtained from the blurring constant calculator 150. The symbol30 denotes a D/A conversion section the same as that described in thefirst embodiment. The D/A conversion section 30 performs a D/Aconversion on the image data D2 that has undergone the temporalfiltering process so as to convert it into a video signal P2 based on aninterlaced format.

Next, the operation of the VDT stress mitigating device according to thethird embodiment will be described according to the flow of the routineshown in FIG. 9.

First, in step S21, the A/D conversion section 10 sequentially importsanalog quantity video signals P1 in an interlaced format from anunillustrated external image signal output device, quantizes these withfields as units, and performs A/D conversion so that the video signalsof each field are converted into digital quantity image data D1. Theimage data D1 is then transferred to the filter section 30.

Next, in step S22, as was described in the second embodiment, the riskquantifying section 100 calculates the risk index e(t) by performing thesteps S11 to S13 shown in FIG. 7, and also holds the image data D1 ofone field imported from the A/D conversion section 10 and outputs thisas image data D10. The risk index value e(t) is transferred to theblurring constant calculator 150.

Next, in step S23, the blurring constant calculator 150 calculates theblurring constant δ (t) from the risk index value e(t) transferred fromthe risk quantifying section 100. At this point, if the risk index valuee(t) is smaller than a preset lower limit threshold value e_(LOW), thevalue of the blurring constant δ is taken as 0. If the risk index valuee(t) is greater than a preset upper limit threshold value e_(HIGH), thevalue of the blurring constant δ is taken as the maximum value δ_(max)described below. If the risk index value e(t) is between the lower limitthreshold value e_(LOW) and the upper limit threshold value e_(HIGH),the value is determined from Formula (4) below, for example. In thiscase, δ_(max) is set as the upper limit value that can be reached by theblurring constant δ, and is a value greater than 0 and less than 1, forexample, 0.7.

[number 2]

The relationship between the risk index value e(t) and the blurringconstant δ (t) is shown in FIG. 10. As is shown in FIG. 10, when therisk index value e(t) is smaller than the lower limit threshold valuee_(LOW), the blurring constant δ (t) is taken as 0. As a result, thefilter section 200 outputs the image data D1 as image data D2 withoutactually performing a filtering process on the image data D1. Becausethere is little possibility of VDT stress being caused when the riskindex value e(t) is small like this, the blurring constant δ is taken as0 thereby giving priority to the quality of the image.

When, on the other hand, the risk index value e(t) is greater than theupper limit threshold value e_(HIGH), the blurring constant δ (t) istaken as the maximum value δ_(max) (for example, 0.7). As a result, thefilter section 200 performs a filtering process on the image data D1using the maximum value δ_(max). Because there is a strong possibilityof VDT stress being caused when the risk index value e(t) is large likethis, the blurring constant δ (t) is taken as the maximum value δ_(max)and the temporal filtering process is performed. However, if theblurring constant δ (t) is too large, the quality of the image cannot bemaintained. Therefore, the blurring constant δ (t) takes the maximumvalue δ_(max) as its upper limit so that the necessary image quality canbe maintained. Moreover, when the risk index value e(t) is between thelower limit threshold value e_(LOW) and the upper limit threshold valuee_(HIGH), the blurring constant δ (t) is set as a value between 0 andthe maximum value δ_(max)according to Formula (4).

Thus, the blurring constant δ (t) is calculated in this way such thatthe risk index value e(t) is reflected therein.

The blurring constants δ (t) may be calculated in advance using Formula(4) and formed into a table for the risk index values e(t) that arelikely to be output from the risk quantifying section 100. It is thuspossible to acquire the blurring constant δ (t) by referring to thistable, based on the risk index values e(t) output from the riskquantifying section 100. Accordingly, the load needed for the blurringconstant δ (t) calculation process can be reduced, and the blurringconstant calculation time can be shortened.

The blurring constant δ (t) determined in the blurring constantcalculator 150 is transferred to the filter section 200 together withthe image data D10 (i.e. I_(i)(t)) of the original image from the fieldmemory 101 of the risk quantifying section 100. At this time, the imagedata D10 is temporally latched in an appropriate manner by the fieldmemory 101 of the risk quantifying section 100, and the timing thereofis matched with that of the blurring constant δ and transferred to thefilter section 200.

Next, in step S24, in the same way as the filter section 20 according tothe first embodiment, the filter section 200 performs a temporalfiltering process on the image data D10 transferred from the riskquantifying section 100 without distinguishing between the first fieldsand second fields and while maintaining the temporal order of eachfield. However, while the filter section 20 according to the firstembodiment performs the temporal filtering process using a presetblurring constant , the filter section 200 according to the thirdembodiment performs the temporal filtering process using blurringconstants δ (t) successively transferred from the blurring constantcalculator 150.

In this case, in the filter section 200, a blurring constant δ (t) usedin the low pass filtering process at the nth stage is transferred to thenext low pass filter together with the field image ^(n)F_(δ)(I_(i)(t))resulting from that process, and the low pass filtering process for thesame original image data is performed using the same blurring constant δ(t).

In the next step S25, the D/A conversion section 30 performs a D/Aconversion such that the image data D2 obtained from the filter section200 is converted into an interlaced format video signal P2 and is thenoutput.

As a result, a series of processes in order to mitigate VDT stress areperformed on interlaced format video signals output from an externalimage signal output device, and the signals are then output to anunillustrated image display device.

According to the third embodiment, the following effects are obtained inaddition to the effects of the above first embodiment.

(1) Because the risk index value e(t) representing the risk of VDTstress is reflected in the blurring constant δ (t) used in the temporalfiltering process, temporal filtering process can be adapted to thelevel of risk and its effects on the image quality can be kept to aminimum.

(2) Because a blurring constant δ (t) and image data corresponding toeach other are transferred to the low pass filter at each stage as agroup, processing that matches the risk index value of each set of imagedata is performed by each low pass filter.

Note that, in the third embodiment, a blurring constant δ (t) istransferred with the corresponding image data through sequential lowpass filters. However, it is also possible, for example, to directlyoutput the blurring constants δ (t) to each low pass filter 201 to 204from the blurring constant calculator 150, and to alter simultaneouslythe blurring constants of each low pass filter stage each time theblurring constants δ (t) output from the blurring constant calculator150 are updated.

Moreover, in the third embodiment, the number of low pass filter stagesin the filter section 200 was set at four. However, the number of stagesmay be reduced to three or less, or may be increased to five or more. Inaddition, the number of low pass filter stages may be set appropriately,in accordance with the necessary filter characteristics.

In addition, in the third embodiment, analog quantity video signals P1are converted into digital quantity image data D1 by the A/D converter10, and digital quantity image data D2 is converted into analog quantityvideo signals P2 by the D/A converter 30. However, as was described inthe first embodiment, these conversion functions can be omitted wherenecessary.

Furthermore, as was described in the first embodiment, it is alsopossible to perform the temporal filtering process using data extendingover three or more fields.

§ 4. Fourth Embodiment

Next, the fourth embodiment of the present invention will be described.

The VDT stress mitigating device according to the fourth embodimentdivides one field into a sub-field comprising odd number columns and asub-field comprising even number columns and performs the temporalfiltering process while for each sub-field.

FIG. 11 shows the structure of the VDT stress mitigating deviceaccording to the fourth embodiment.

As is shown in FIG. 11, in the structure according to the firstembodiment shown in FIG. 1, the VDT stress mitigating device accordingto the fourth embodiment is further provided with a field dividingsection 15 between the A/D conversion section 10 and the filter section20, for dividing each field into a sub-field comprising an odd numbercolumn (referred to below as an odd number sub-field) and a sub-fieldcomprising an even number column (referred to below as an even numbersub-field). The VDT stress mitigating device according to the fourthembodiment is also provided with field synthesizing section 25 betweenthe filter section 20 and the D/A conversion section 30 for synthesizingeach field from the sub-fields.

Next, the operation of the VDT stress mitigating device according to thefourth embodiment will be described according to the flow of the routineshown in FIG. 12.

First, in step S31, the A/D conversion section 10 sequentially importsanalog quantity video signals P1 in an interlaced format from anunillustrated external image signal output device, quantizes these withfields as units, and performs A/D conversion so that the video signalsof each field are converted into digital quantity image data D1. Theimage data D1 of each field is then transferred to the field dividingsection 15.

Next, in step S32, the field dividing section 15 divides the image dataD1 of each field into an odd number sub-field and an even numbersub-field. This field dividing is performed by sampling every secondpixel on each line. The field dividing section 15 takes an odd numbersub-field and an even number sub-field as a pair, and sequentiallyoutputs to the filter section 20 the image data D 11 of each sub-fieldat a temporal frequency twice the temporal frequency of the field.

Next, in step S33, in the same way as in the above first embodiment, thefilter section 20 performs a temporal filtering process on the imagedata D 11 of each sub-field divided by the field dividing section 15without distinguishing between sub-fields belonging respectively to thefirst fields and second fields and while maintaining the temporal orderof each sub-field. As a result the image data D22 is generated.

At this stage, the corresponding relationship between the pixels in eachsub-field and the pixels in each frame in the temporal filtering processwill be described with reference made to FIG. 13.

In the example shown in FIG. 13, the first field f1 forming the frame Fis divided into an odd number sub-field f1 a and an even numbersub-field f1 b. In the same way, the second field f2 forming the frame Fis divided into an odd number sub-field f2 a and an even numbersub-field f2 b. Specifically, each field forming the frame F is dividedin layers so that the frame F is divided into the four sub-fields f1 a,f1 b, f2 a, and f2 b. The image data D11 of these sub-fields istransferred to the filter section 20.

Note that, in the fourth embodiment, the temporal order of eachsub-field in each frame is in the order f1 a→f1 b→f2 a→f2 b. However, atthe limit where the temporal order of the first field and second fieldcan be maintained, the temporal order of the sub-field within one framecan be settled in any manner.

The pixels P1 a, P1 b, P2 a, and P2 b within the frame F shown in FIG.13 will now be looked at. The pixels P1 a and P1 b belong to the firstfield and are contiguous to each other. The pixels P1 b and P2 b belongto the second field and are contiguous to each other. Moreover, thepixels P1 a and P1 b and the pixels P2 a and P2 b belong to lines thatare contiguous to each other. Further, the pixels P1 a and P2 a belongto the odd number column, while the pixels P2 a and P2 b belong to theeven number column.

Because, at present, there is no distinction made between the firstfield and second field, in this case, the pixels P1 a and P1 b thatbelong to the first field and the pixels P2 a and P2 b that belong tothe second field correspond to each other. Moreover, as a result of thedividing of the first field, the pixels P1 a that belong to the oddnumber sub-field f1 a and the pixels P1 b that belong to the even numbersub-field f1 b correspond to each other. As a result of the dividing ofthe second field, the pixels P2 a that belong to the odd numbersub-field f2 a and the pixels P2 b that belong to the even numbersub-field f2 b correspond to each other. Specifically, these four pixelsare pixels of positions that correspond to each other on undistinguishedsub-fields.

A temporal filtering process is performed on the pixels P1 a, P1 b, P2a, and P2 b that correspond to each other in the above temporal order(f1 a→f1 b→f2 a→f2 b). Specifically, first, the respective image data ofthe pixel P1 a and the pixel P1 b are set as the subjects of thetemporal filtering process using the above Formulas (1) and (2). Becausethe pixels P1 a and P1 b are pixels on adjacent columns on the same linein the first field, the frequency components in the horizontal directionof the screen of the first field are attenuated by this process, andblurring is generated in the horizontal direction.

Next, the respective image data of the pixel P1 b and the pixel P2 a areset as the subjects of the temporal filtering process using the aboveFormulas (1) and (2). Because the pixels P1 b and P2 a are pixels onadjacent lines, the frequency components in the vertical direction ofthe screen are attenuated by this process, and blurring is generated inthe vertical direction.

Next, the respective image data of the pixel P2 a and the pixel P2 b areset as the subjects of the temporal filtering process using the aboveFormulas (1) and (2). Because the pixels P2 a and P2 b are adjacentpixels on the same line in the second field, the frequency components inthe horizontal direction of the screen of the second field areattenuated by this process, and blurring is generated in the horizontaldirection.

Next, the last pixel P2 b is set as the object of the temporal filteringprocess using the above Formulas (1) and (2) together with the pixel p1a belonging to the first field of the next frame. The above pixels P1 a,P1 b, P2 a, and P2 b are then set as repeating units for processing andthe same temporal filtering process is then performed on each of thesepixels.

Moreover, this processing that is performed with the pixels P1 a, P1 b,P2 a, P2 b of each sub-field as repeating units is performed in parallelfor all the pixels in each sub-field and is a series of temporalfiltering processes that is performed over the total screen.

The image data D22 obtained by performing a temporal filtering processon the image data D11 of each sub-field in this way is transferred tothe field synthesizing section 25.

Next, in step S34, the field synthesizing section 25 follows a procedurethat is the reverse of the dividing procedure shown in FIG. 13 andsynthesizes the respective image data D22 of the odd number sub-fieldsand the even number sub-fields into image data D2 of each field. Thatis, the original field image data is reconstructed by combining togetherevery second pixel on each line from the image data of the twosub-fields, i.e. the odd number column and the even number column,forming the same field sequentially output from the filter section 20.

Next, in step S35, the D/A conversion section 30 performs a D/Aconversion on the image data D2 obtained from the field synthesizingsection 25 so that this is converted into interlaced format videosignals P2 that are then output. In this processing by the D/A converter30, the temporal order of the two sub-fields forming the same field ismaintained.

As a result of the above, a series of processes for mitigating VDTstress is performed on interlaced format video signals output from anexternal image signal output device, and these signals are then outputto an unillustrated image display device.

According to the fourth embodiment, in addition to the effects of thefirst embodiment, the below effects are also achieved.

(1) Because each field is divided into an odd number sub-field and aneven number sub-field and a temporal filtering process is performed oneach sub-field, it is possible to attenuate frequency components in thehorizontal direction of the screen and frequency components in thevertical direction of the screen, and it is thus possible to effectivelymitigate VDT stress.

(2) Moreover, because a temporal filtering process is performed on eachsub-field, it is possible to reduce the size of the buffer memory forimage data of each low pass filter forming the filter section 20.

Note that, in the fourth embodiment, the first field was divided intotwo sub-fields. However, it is also possible for the dividing to beperformed in even smaller units and to set the number of divisions tomeet requirements. If the number of field divisions is increased, thespatial filtering effect is striking and it becomes possible to evenmore effectively mitigate VDT stress using a regular spatial pattern

Moreover, it is also possible to combine the VDT stress risk quantifyingdevice according to the second embodiment with the VDT stress mitigatingdevice according to the fourth embodiment.

Furthermore, in the fourth embodiment, the A/D conversion process andthe field dividing process were performed separately. However, it isalso possible, for example, to separate and extract video signals of theodd number columns and the even number columns and to perform the A/Dconversion process on each respectively. In fact, any means may be usedprovided that the result thereof allows the obtaining of image data inwhich one field is divided into an odd number sub-field and an evennumber sub-field. In the same way, any means may also be employed forthe D/A conversion process and the field synthesizing process.

Moreover, in the fourth embodiment, the number of low pass filter stagesin the filter section 20 was set at four. However, the number of stagesmay be reduced to three or less, or may be increased to five or more. Inaddition, the number of low pass filter stages may be set appropriately,in accordance with the necessary filter characteristics.

In addition, in the fourth embodiment, analog quantity video signals P1are converted into digital quantity image data D1 by the A/D converter10, and digital quantity image data D2 is converted into analog quantityvideo signals P2 by the D/A converter 30. However, as was described inthe first embodiment, these conversion functions can be omitted wherenecessary.

Furthermore, as was described in the first embodiment, it is alsopossible to perform the temporal filtering process using data extendingover three or more fields, or to perform a spatial filtering processingin combination therewith.

The first through fourth embodiments of the present invention have beendescribed above. However, the present invention is not limited to theseembodiments, and, provided that a temporal filtering process isperformed without a distinction being made between fields, then any suchstructure is included in the scope of the present invention. Moreover,any alteration in design that does not depart from the intention of thisinvention is also included within the scope of the present invention.For example, in the above embodiments, the device was realized ashardware. However, it may also be realized as software. In this case, ifa program describing the functions of the device is recorded on arecording medium, then it is possible to construct the VDT stressmitigating device according to the present invention on a computer or totransfer it to another computer.

As has been described above, according to the present invention, thefollowing effects can be obtained.

This means that because a temporal filtering process is performed on theimage signals of each of a first and second field without anydistinction being made between these fields and while the temporal orderof these fields is maintained, temporal and spatial filtering processesare performed on the image signals and it is possible to mitigate VDTstress caused by a regular spatial pattern and VDT stress caused byflicker due to the interlaced format.

Moreover, because an index value representing the risk of VDT stressfrom image signals is calculated thus allowing the stress to bequantified, and because the index value is reflected and predeterminedfrequency components included in the image signals are attenuated suchthat the risk is suppressed, it is possible to mitigate VDT stress inaccordance with the degree of the risk of VDT stress.

Further, because each field of an image signal is divided into aplurality of sub-fields, and a temporal filtering process is performedon the image signals of each sub-field without any distinction beingmade between the plurality of sub-fields and while the temporal order ofthe sub-fields is maintained, a spatial filtering process is performedin a screen horizontal direction and in a screen vertical direction, andit is possible to more effectively mitigate VDT stress.

Furthermore, because an image signal is imported and held temporarily,and because a temporal filtering process is performed on the imagesignals of each of a first and second field without any distinctionbeing made between these fields and while the temporal order of thesefields is maintained, and because an index value representing the riskof VDT stress is calculated on the basis of the difference between theimage signal that has undergone the temporal filtering process and theheld image signal, it is possible to quantify the risk of VDT stress andto detect this risk.

1. The VDT stress mitigating device according to claim 1, wherein thefilter means comprises: a signal importing section for sequentiallyimporting the image signals in units of fields; a field dividing sectionfor dividing each field of the image signals into a plurality ofsub-fields; a low pass filter section for performing a temporalfiltering process on image signals of each sub-field withoutdistinguishing between the plurality of sub-fields and while maintainingthe temporal order of the sub-fields, and for attenuating predeterminedfrequency components contained in an image formed by the image signals;a field synthesizing section for synthesizing image signals of eachfield from image signals of each sub-field in which the predeterminedfrequency components have been attenuated; and a signal output sectionfor sequentially outputting in accordance with the temporal order theimage signals of each field that have been synthesized by the fieldsynthesizing section.
 2. A VDT stress mitigation method for mitigatingVDT stress by attenuating predetermined frequency components of imagesignals based on an interlaced format, comprising the following steps:(a) a signal importing step in which the image signals are sequentiallyimported in units of fields; (b) a field dividing step in which eachfield of the image signals is divided into a plurality of sub-fields;(c) a filtering step in which a temporal filtering process is performedon image signals of each sub-field without distinguishing between theplurality of sub-fields and while maintaining the temporal order of thesub-fields, and for attenuating predetermined frequency componentscontained in an image formed by the image signals; (d) a fieldsynthesizing step for synthesizing image signals of each field fromimage signals of each sub-field in which the predetermined frequencycomponents have been attenuated; and (e) a signal output step in whichsynthesized image signals of each field are sequentially output inaccordance with the temporal order.
 3. The VDT stress mitigation methodaccording to claim 13, wherein, in the filtering step, temporalfrequency components that are contained in an image formed by the imagesignals and that are equivalent to a frame scan frequency areattenuated.
 4. The VDT stress mitigation method according to claim 13,wherein, in the filtering step, spatial frequency components that arecontained in an image formed by the image signals and that are thehighest spatial frequency components in a direction orthogonal to a scanline direction on a device on which the image is displayed areattenuated.